1. Field of Art
This invention relates to pressurized containers and in particular to means for forming a vent opening in the wall of a pressurized container to release the pressure therein.
2. Brief Description of the Prior Art
It is known to form an embossed rib in a container wall with a transverse score line across the rib to facilitate rupture of the container wall as is disclosed in an application for United States Letters Patent Ser. No. 684,836, filed May 10, 1976 for "Container Wall with Rupturable Weakening Line". The combination of an embossed hollow rib and a transverse score line acts in a manner similar to a notched beam. In a container wall having an embossed rib therein with a score line across the rib, the score line can be easily ruptured by applying force against the rib at the score line on the side of the container wall opposite that from which the rib projects. The score line weakens the side of the rib which is in tension under such loading so the rib and score line can be easily broken. Conversely, pressure applied against the container wall on the side thereof from which the rib projects does not easily rupture the score line because such loading places the residual metal in the score line in compression rather than tension. An embossed rib and transverse score line may be employed in a container wall either to facilitate rupture of the wall by digitally applied force or by excessive pressure in a container.
In recent years, the widespread use of metal easy-opening cans having severable tear strips has created a litter problem due to the propensity of consumers to indiscriminately dispose of the severed tabs. Consequently, considerable time and money have been expended to develop easy-opening can ends having non-severable tear tabs and tear strips. As a result, a number of easy-opening ends have been developed which have inwardly displaceable tabs as for example are disclosed in U.S. Pat. Nos. 3,362,569; 3,881,630; 3,886,881 and 3,929,251, among others. However, the force required to open push-in tabs in can ends has heretofore been affected by the internal pressure in the cans. To minimize the effect of the internal pressure, a smaller opening tab has been provided in some can ends to initially vent the internal pressure as is disclosed in U.S. Pat. No. 3,741,432. However, even a small tab in a can end is affected by the pressure and can be difficult to open.
A digitally operable pressure release device is desired for easy-opening can ends and other containers which will not be affected by the internal pressure in the container.